1. Field of the Invention
The present invention mainly relates to a touch panel used for an operation of various electronic devices.
2. Background Art
In recent years, various electronic devices such as a mobile phone and a car navigation system having more sophisticated and diversified functions have increasingly incorporate therein an optically-transparent touch panel attached to a front face of a display element (e.g., liquid crystal). A user of such an electronic device depresses and operates the touch panel by a finger or a pen while visually recognizing, through the touch panel, the display on the display element at the back face of the touch panel. Through this operation, the respective functions of the electronic device are switched. Thus, such a touch panel has been required that has a superior visibility and that provides secure operation and electric connection.
A conventional touch panel will be described with reference to FIG. 8 to FIG. 10.
FIG. 8 is a cross-sectional view illustrating a conventional touch panel. FIG. 9 is a plan view illustrating an upper substrate used for the touch panel shown in FIG. 8. FIG. 10 is a plan view illustrating a lower substrate used for the touch panel shown in FIG. 8. In FIG. 8 to FIG. 10, upper substrate 101 has a film-like shape and is optically-transparent. Upper substrate 101 has, at a lower side thereof, optically-transparent lower substrate 102. On a lower surface of upper substrate 101, optically-transparent upper conductive layer 103 is formed by material such as indium tin oxide. On an upper surface of lower substrate 102, optically-transparent lower conductive layer 104 is similarly formed by material such as indium tin oxide for example.
Both ends of upper conductive layer 103 have a pair of upper electrodes 105, 106. Both ends of lower conductive layer 104 have a pair of lower electrodes 107, 108 formed in a direction orthogonal to upper electrodes 105, 106. Upper electrodes 105, 106 extend along an outer periphery of upper conductive layer 103. End of upper substrate 101 has a plurality of lead sections 105a, 106a. Lower electrodes 107, 108 extend along an outer periphery of lower conductive layer 104. End of lower substrate 102 has a plurality of lead sections 107a, 108a. It is noted that upper electrodes 105, 106 and lower electrodes 107, 108 are made of conductive material including silver.
Slit 109 is provided at an inner side of upper electrodes 105, 106 and between lead sections 105a, 106a. Slit 109 having a substantially T-like shape is obtained by removing upper conductive layer 103 by a method including a laser cutting or an etching processing, for example. Slit 110 is also provided between lower electrodes 107, 108, and between lead sections 107a, 108a. Slit 110 having a substantially L-like shape is similarly obtained by removing lower conductive layer 104 by the method including a laser cutting or an etching processing, for example. This prevents the short circuiting between upper electrode 105 and upper electrode 106, and between lower electrode 107 and lower electrode 108, thereby securing insulation among the electrodes.
At an upper surface of lower conductive layer 104, a plurality of dot spacers (not shown) made of insulating resin are formed with a predetermined interval thereamong. Spacer 111 having a substantially frame-like shape is provided at an outer periphery of a lower face of upper substrate 101 or an outer periphery of an upper face of lower substrate 102. An upper face and a lower face of spacer 111 are coated with adhesion layers (not shown). As a result, an outer periphery of upper substrate 101 is adhered with an outer periphery of lower substrate 102 and upper conductive layer 103 is facing to lower conductive layer 104 with a predetermined space therebetween. In this manner, touch panel 100 is provided.
Touch panel 100 thus structured is placed on a front face of a liquid crystal display element (not shown) and others, and is attached to an electronic device. Lead sections 105a, 106a, 107a, and 108a provided at end sections of upper electrodes 105, 106 and end sections of lower electrodes 107, 108 are connected to an electronic circuit of an electronic device (not shown) via a wiring substrate (not shown) in which upper and lower faces have a plurality of wiring patterns, for example.
In the structure as described above, an upper face of upper substrate 101 is depressed and operated by a finger or a pen while the display of a liquid crystal display element provided at the back face of touch panel 100 being visually recognized. As a result, upper substrate 101 is bent and upper conductive layer 103 at the depressed portion is come into contact with lower conductive layer 104.
Then, a voltage is sequentially applied from the electronic circuit via the wiring substrate to upper electrodes 105, 106 as well as lower electrodes 107, 108. The applied voltage is sequentially applied to the both ends of upper conductive layer 103 and the both ends of lower conductive layer 104 in a direction orthogonal to upper conductive layer 103. Based on a voltage ratio of upper electrodes 105, 106 and a voltage ratio of lower electrodes 107, 108, the depressed position is detected by the electronic circuit. As a result, various functions of the electronic device are switched.
In touch panel 100 having the conventional structure as described above, slits 109, 110 are formed by the method including a laser cutting or an etching processing as described above. Among them, a laser cut processing has been increasingly used in recent years because it provides a speedy manufacture. However, when slit 109 is formed by a laser cut processing, for example, the processing is actually performed to cause protruded section 109b, as shown in FIG. 9, that inwardly protrudes from intersection 109a having a substantially T-like shape. Specifically, protruded section 109b is caused by the control of a laser beam for machining slit 109.
When a strong force is applied to a position adjacent to intersection 109a as shown in FIG. 9 or terminal section 110a of slit 110 as shown in FIG. 10 for example, or when such a part is subjected to a depression operation repeated for a long time, this part may crack or break to cause a crack or breakage of upper conductive layer 103 and lower conductive layer 104. This causes unstable electrical connection and separation between upper conductive layer 103 and lower conductive layer 104.
To prevent such a situation, slit 109 is formed by a laser beam with a slowly controlled moving speed so that the laser beam does not move beyond intersection 109a, although the moving speed causes a longer manufacture time. Alternatively, a part adjacent to intersection 109a and a part adjacent to terminal section 110a are covered by spacer 111, although the existence of spacer 111 reduces an operation region, for example.
A conventional touch panel is disclosed, for example, in Japanese Patent Unexamined Publication No. 2003-58319.